Physicochemical characterization of the polysaccharide from Bletilla striata: effect of drying method

The polysaccharide from Bletilla striata, a traditional Chinese herbal medicine, was obtained by different drying techniques: vacuum-drying (BVPS) or vacuum freeze-drying (BFPS). The effect of drying method on the physicochemical properties of the B striata polysaccharide was evaluated using high size exclusion chromatography coupled to multiangle laser light scattering (HPSEC-MALLS), FT-IR and UV spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The monosaccharide analysis and pH test revealed that the polysaccharide derived from B. striata was a neutral polysaccharide that is composed of glucose and mannose. The solubility and moisture content test's results demonstrated that BFPS was greater than BVPS. The number average molecular weight (Mn) and the computed average molecular weight (Mw) of 99.3% BFPS were 7.297×10(4)g/mol and 9.545×10(4)g/mol, respectively, whereas the Mn and Mw of 97.6% BVPS were 1.218×10(5)g/mol and 1.472×10(5)g/mol, respectively. The FT-IR and UV results indicated that drying technique has little effect on the structure of the polysaccharide. The thermal analysis showed that weight loss event was at 307.85°C and 305.50°C to BVPS and BFPS, respectively. Furthermore, the XRD confirmed that the polysaccharide was the amorphous nature. However, both SEM and AFM images exhibited that the drying technique had a significant impact on the morphology and conformation of the polysaccharide.